1. Technical Field
This invention relates generally to dynamic oil seals of the type for creating a fluid tight seal between a rotating shaft and housing.
2. Related Art
Dynamic radial shaft oil seals are designed to have a so-called “oil side” of the seal and an “air side.” These designations pertain to the orientation of the seal when installed, with the oil side facing the interior of the housing and in communication with the oil, whereas the air side faces outwardly and is exposed to the air.
There are at least two different ways in which a radial shaft oil seal can be installed. An “air side installation” is one type of assembly in which the seal is first installed into the bore of the housing and the shaft (or its wear sleeve) is thereafter installed from the air side axially into the seal assembly (in the direction inward of the housing) to effect the seal. An “oil side installation” is the other way of assembly where the housing and shaft are already present and the seal assembly is slid axially into the housing and simultaneously onto the shaft (or its wear sleeve), such that the shaft enters the seal assembly from the oil side of the seal. Otherwise, “oil-side” installation requires the seal assembly to be installed into the housing, also referred to as carrier, and then the housing, with seal installed therein, is assembled to an engine over the “all ready in place” shaft wherein the shaft enters the seal from the oil side of the seal.
During installation, regardless of the type, the seals must be able to withstand the axial loads resulting during installation without causing a seal lip of the seal to reverse fold or otherwise become displaced to a position where the seal lip is ineffective in the fully installed condition.
Radial shaft seals are also subject to varying axial pressures that can be seen during leak testing or in use. The pressure differential developed across the seal (across the oil and air sides of the seal) can impart an axial load on the seal in one direction or the other (a vacuum or increased pressure in the housing) and can cause the seal to pull away from the shaft to at least some degree, and in extreme cases can cause the seal to reverse fold and collapse under the pressure so that the seal against the shaft or wear sleeve is broken.